As MEMS (Micro-Electro-Mechanical-System) sensors, navigation, and control technology develop, combined with increasing government support for agriculture, has led to precision agriculture becoming increasingly popular. During agricultural machine-assisted driving control, the motion and position information of the vehicle body can be reflected by the attitude (including pitch angle, the roll angle, and course angle), speed, and position information of the vehicle body in real time. This information can provide important data input for a combined navigation and control algorithm with high-precision.
Strapdown-Inertial-Navigation-System (SINS) has features such as: autonomous navigation, good confidentiality, strong anti-interference ability, having plentiful navigation parameters, having high precision for using in a short period time, etc., and is widely used. However, since the inertial sensor has inherent errors, as time goes by, navigation errors accumulate and the accuracy of the navigation deteriorates, such that the assistant of other navigation systems (e.g. a high-precision GPS-RTK) with stable error are required. The inertial navigation system obtains velocity and position information by carrying out an integral operation based on the measured acceleration of the vehicle body. Hence, it is necessary to know initial velocity and position. Additionally, in an inertial navigation system taking the geographic coordinate system as a navigation coordinate system, either the physical platform or the mathematical platform is a reference for measuring the acceleration. Furthermore, the platform must accurately align and track the geographic coordinate system to avoid the error of the platform from causing the error in acceleration measurement. The accuracy of initial alignment directly relates to the working accuracy of the navigation system. Thus, the initial alignment is also one of the key technologies.
There are two commonly used alignment methods: coarse alignment and alignment. However, the two alignment methods are mainly used with high-precision gyroscopes, which can sense the angular speed of Earth's rotation. Therefore, these two alignment methods are not suitable for the inertial navigation apparatus with a low-cost and low-performance.